The failure of the heart to provide adequate circulation of blood is a serious life-threatening problem. Heart transplants have treated the most serious cases of heart failures. A heart transplants though is a drastic procedure with high risk and the supply of donors is limited when compared to the total need. Considerable research and development has been done therefore into developing artificial hearts that can replace the human heart. Currently most artificial heart blood pumping systems are used more as temporary heart assistants pending the location of a heart donor.
A variety of functional designs for artificial hearts are in the patent prior art and a number of functional designs now exist and are in use at various heart centers around the world. The AbioCor™ implantable replaceable heart, provided by ABIOMED, Inc. is a self-contained implantable replacement heart. This pump weighs about two pounds and consists of artificial ventricles that contain corresponding valves and a motor driven hydraulic pumping system. The hydraulic pumping system uses pressure to move blood from the artificial right ventricle to the lungs or from the artificial left ventricle to the rest of the body. To create this pressure the pump motor rotates at 4000 to 8000 rpm. Another system, the ABIOMED BVS-5000 is an air driven dual chamber blood pump placed outside the body used primarily for temporary left, right, or biventricular support of patients with heart failure. The pump houses two polyurethane chambers, an atrial chamber that fills with blood through gravitational force and a ventricle chamber that pumps blood by air-driven power. Two trileaflet valves separate the chambers.
The Thoratec HeartMate® implantable pneumatic left ventricular assist system is based on an air-driven titanium alloy pump that weighs about 570 grams and consists of a blood chamber, an air chamber, a drive line and inflow and outflow conduits. Each conduit is a titanium cage that contains a valve within a Dacron fabric graft. The pump is powered and controlled by an external portable console. The Thoratec HeartMate II® is an implantable left ventricular assist system based on a continuous axial flow in-line pump. There are other artificial blood pumping systems under development and in use.
The existing solutions have provided utility and prolonged lives. There are still many issues to be addressed however. Many of the prior solutions provide continuous flow whereas a problem free pulsatile flow that provides a more physiologic flow of blood is needed. Pulsatile flow is sometimes provided by flexible-volume chambers (bladders, tubing, bellows) but these are susceptible to wear and prone to thrombosis. Thrombosis as related to medical devices is the formation of blood clots on, or inside of, a medical device, and can lead to serious consequences. Flexible-volume chambers that do not completely or nearly completely expel their contained fluid during each stroke can also be prone to thrombosis. Another issue is simply size. Pumping systems with multiple chambers and the accompanying drive mechanism are typically too large to fit in smaller adults or children. Partially related to size is energy efficiency, with these systems requiring too much energy to operate. In addition to size though, many designs are inherently energy inefficient because of mechanisms that require reversing motion (pistons, bladders) that expends additional energy. Another issue evident from the above discussion of some of the existing systems is the use of valves. Valves not only add to size and complexity (and therefore reliability) but also are prone to calcification, wearing out and to thrombosis. Some of the prior art systems and devices also have problems with hemolysis (breakdown of red blood cells) due to either mechanical forces or shear forces in the motion of the fluid. Finally there is a definite need for easier flow modification of blood pumping systems. Many of the existing systems require separate drive force or shunting to accomplish this. Additionally, none of the prior art devices are known to provide two streams with simultaneous discharge pulsation peaks or simultaneous intake strokes, which simultaneity is physiologically desirable.
The above needs can be addressed by applying modifications of new pumping technology to the special problems of blood pumping systems.
Spherical rotary pumping systems have been developed that consist of a spherical housing within which one or more vanes rotate. This is in contrast to those devices that utilize a reciprocating, linearly moving piston. In the case of the spherical rotary pumps the vanes are rotated by a shaft to cause the fluid to flow through the device.
U.S. Pat. No. 5,199,864 to Stecklein discloses a rotary fluid pump that employs vanes rotating within a spherical housing and includes an interior carrier ring that guides a particular motion of the vanes so that they open and close to draw in and either pump or compress fluids, thereby creating a type of pulsatile flow. This patent also describes an embodiment (the “second embodiment”) that uses an exterior carrier ring to guide the reciprocal motion of the vanes. These devices are highly efficient, and are capable of displacing large quantities of fluid relative to their size, so that the use of a small pump is possible. The flow of fluid is typically controlled by the rate at which the rotary vanes are rotated. By increasing the speed, more fluid is pumped through the device, while decreasing the speed decreases the amount of fluid pumped.
U.S. Pat. No. 6,241,493 to Turner discloses a particularly useful improvement on this type of spherical fluid machine that is configured to enable adjustments in both fluid capacity and fluid direction without changing the speed or direction of rotation of the vanes in the device by adjusting the orientation of an interior carrier ring. That patent is incorporated by reference into this application.
Fluid machines such as that described in U.S. Pat. No. 6,241,493 and U.S. Pat. No. 5,199,864 are also already ported, meaning that the manner in which the chambers communicate with the inlet and discharge ports negates the need for valves. They can be especially long running from a maintenance perspective because there is no direct physical contact between either the vanes and the central sphere around which they rotate nor physical contact between the vanes and the exterior housing of the machine. Low leakage between chambers is achieved by maintaining small clearances that minimize slippage or fluid loss across the clearances.
Further improvements to these types of spherical rotary pumps are disclosed in U.S. patent application Ser. No. 10/784,709 by the inventor of the instant invention and that application is incorporated herein by reference in its entirety. These improvements included adding stability to the design, adding internal cooling, incorporating the ability to pump multiple fluids, and adding critical seals. Some of these improvements were aimed at the dual use of this type of a pump as a fluid pump as well as a compressor and/or motor in industrial applications. It is important to note that none of the prior art references on these spherical rotary pumps recognized their potential value as an artificial heart or as a ventricular assist device nor were the particular issues inherent in adapting this solution for those applications recognized or dealt with in these references. For example, issues related to biocompatibility, hemocompatibility, hemolysis and thrombosis were not addressed. The crux of the instant invention is the recognition of the need and the adaptation of these devices for this application.